function getViewportSize() {

}

//检测滚动条是否滚动到页面底部
export function isScrollToPageBottom(){
    //文档高度
    var documentHeight = document.documentElement.offsetHeight;
    var viewPortHeight = getViewportSize().h;
    var scrollHeight = window.pageYOffset ||
        document.documentElement.scrollTop ||
        document.body.scrollTop || 0;

    return documentHeight - viewPortHeight - scrollHeight < 20;
}
